libinstaller/setadv.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 2007-2008 H. Peter Anvin - All Rights Reserved
   4  *   Copyright 2010 Intel Corporation; author: H. Peter Anvin
   5  *
   6  *   This program is free software; you can redistribute it and/or modify
   7  *   it under the terms of the GNU General Public License as published by
   8  *   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
   9  *   Boston MA 02111-1307, USA; either version 2 of the License, or
  10  *   (at your option) any later version; incorporated herein by reference.
  11  *
  12  * ----------------------------------------------------------------------- */
  13
  14 /*
  15  * setadv.c
  16  *
  17  * (Over)write a data item in the auxilliary data vector.  To
  18  * delete an item, set its length to zero.
  19  *
  20  * Return 0 on success, -1 on error, and set errno.
  21  *
  22  */
  23 #define  _GNU_SOURCE
  24
  25 #include <stdio.h>
  26 #include <stdlib.h>
  27 #include <stddef.h>
  28 #include <stdint.h>
  29 #include <string.h>
  30 #include <errno.h>
  31 #include "syslxint.h"
  32 #include "syslxcom.h"
  33 #include "syslxfs.h"
  34
  35 unsigned char syslinux_adv[2 * ADV_SIZE];
  36
  37 #define ADV_MAGIC1      0x5a2d2fa5      /* Head signature */
  38 #define ADV_MAGIC2      0xa3041767      /* Total checksum */
  39 #define ADV_MAGIC3      0xdd28bf64      /* Tail signature */
  40
  41 static void cleanup_adv(unsigned char *advbuf)
  42 {
  43     int i;
  44     uint32_t csum;
  45
  46     /* Make sure both copies agree, and update the checksum */
  47     set_32((uint32_t *) advbuf, ADV_MAGIC1);
  48
  49     csum = ADV_MAGIC2;
  50     for (i = 8; i < ADV_SIZE - 4; i += 4)
  51         csum -= get_32((uint32_t *) (advbuf + i));
  52
  53     set_32((uint32_t *) (advbuf + 4), csum);
  54     set_32((uint32_t *) (advbuf + ADV_SIZE - 4), ADV_MAGIC3);
  55
  56     memcpy(advbuf + ADV_SIZE, advbuf, ADV_SIZE);
  57 }
  58
  59 int syslinux_setadv(int tag, size_t size, const void *data)
  60 {
  61     uint8_t *p;
  62     size_t left;
  63     uint8_t advtmp[ADV_SIZE];
  64
  65     if ((unsigned)tag - 1 > 254) {
  66         errno = EINVAL;
  67         return -1;              /* Impossible tag value */
  68     }
  69
  70     if (size > 255) {
  71         errno = ENOSPC;         /* Max 255 bytes for a data item */
  72         return -1;
  73     }
  74
  75     left = ADV_LEN;
  76     p = advtmp;
  77     memcpy(p, syslinux_adv + 2 * 4, left);      /* Make working copy */
  78
  79     while (left >= 2) {
  80         uint8_t ptag = p[0];
  81         size_t plen = p[1] + 2;
  82
  83         if (ptag == ADV_END)
  84             break;
  85
  86         if (ptag == tag) {
  87             /* Found our tag.  Delete it. */
  88
  89             if (plen >= left) {
  90                 /* Entire remainder is our tag */
  91                 break;
  92             }
  93             memmove(p, p + plen, left - plen);
  94         } else {
  95             /* Not our tag */
  96             if (plen > left)
  97                 break;          /* Corrupt tag (overrun) - overwrite it */
  98
  99             left -= plen;
 100             p += plen;
 101         }
 102     }
 103
 104     /* Now (p, left) reflects the position to write in and how much space
 105        we have for our data. */
 106
 107     if (size) {
 108         if (left < size + 2) {
 109             errno = ENOSPC;     /* Not enough space for data */
 110             return -1;
 111         }
 112
 113         *p++ = tag;
 114         *p++ = size;
 115         memcpy(p, data, size);
 116         p += size;
 117         left -= size + 2;
 118     }
 119
 120     memset(p, 0, left);
 121
 122     /* If we got here, everything went OK, commit the write */
 123     memcpy(syslinux_adv + 2 * 4, advtmp, ADV_LEN);
 124     cleanup_adv(syslinux_adv);
 125
 126     return 0;
 127 }
 128
 129 void syslinux_reset_adv(unsigned char *advbuf)
 130 {
 131     /* Create an all-zero ADV */
 132     memset(advbuf + 2 * 4, 0, ADV_LEN);
 133     cleanup_adv(advbuf);
 134 }
 135
 136 static int adv_consistent(const unsigned char *p)
 137 {
 138     int i;
 139     uint32_t csum;
 140
 141     if (get_32((uint32_t *) p) != ADV_MAGIC1 ||
 142         get_32((uint32_t *) (p + ADV_SIZE - 4)) != ADV_MAGIC3)
 143         return 0;
 144
 145     csum = 0;
 146     for (i = 4; i < ADV_SIZE - 4; i += 4)
 147         csum += get_32((uint32_t *) (p + i));
 148
 149     return csum == ADV_MAGIC2;
 150 }
 151
 152 /*
 153  * Verify that an in-memory ADV is consistent, making the copies consistent.
 154  * If neither copy is OK, return -1 and call syslinux_reset_adv().
 155  */
 156 int syslinux_validate_adv(unsigned char *advbuf)
 157 {
 158     if (adv_consistent(advbuf + 0 * ADV_SIZE)) {
 159         memcpy(advbuf + ADV_SIZE, advbuf, ADV_SIZE);
 160         return 0;
 161     } else if (adv_consistent(advbuf + 1 * ADV_SIZE)) {
 162         memcpy(advbuf, advbuf + ADV_SIZE, ADV_SIZE);
 163         return 0;
 164     } else {
 165         syslinux_reset_adv(advbuf);
 166         return -1;
 167     }
 168 }